1. Field of the Invention
This invention relates to a sensor-equipped rolling bearing apparatus.
2. Related Art
In the measurement of a rotational motion in various apparatuses, there are cases where a measurement mechanism is provided on a bearing apparatus. For example, when there is provided an ABS (anti-lock braking system) for a vehicle axle drive wheel, an ABS sensor for detecting a rotational speed is often fixed to a bearing apparatus. In this case, the ABS sensor is fixed to a cover member fitted on an outer periphery of a stationary ring of the bearing, and the ABS sensor detects the rotational speed on the basis of a change of a magnetic flux density caused by the rotation of a magnet rotor (magnetic member) fitted on a rotating ring of the bearing.
In the type of structure in which an encoder made of a permanent magnet is fixed to a rotating ring of a bearing for rotatably supporting a drive wheel of a vehicle, foreign matters and others picked up during the travel of the vehicle deposit on a surface of the encoder to thereby adversely affect the detection ability for the rotational speed unless the an inner peripheral portion of a knuckle (which supports and fixes a bearing apparatus) and an axle, thereby isolating an encoder from an external space so that foreign matters will not deposit on the encoder.
In the technique of JP-A-2001-147252, although the encoder can be isolated from the exterior by the seal ring, a sliding resistance develops since the seal ring is disposed in sliding contact with the rotating axle and the fixed portion. This offers a resistance to the driving of the vehicle, and therefore is an obstacle to the achievement of a low fuel consumption. This is a great drawback in view of the fact that there is an increasing demand for improving the performance of vehicles.
Therefore, it is necessary to provide a bearing apparatus of the type in which the conventional technique is improved without degrading the bearing performance so that the magnetic member will not be exposed to the exterior. In one typical ABS mounting method heretofore extensively used, a cover member is fitted to a stationary ring of a rolling bearing, and for fixing an ABS sensor to the cover member, a pressing portion for pressing the ABS sensor by its elastic deformation is formed at the cover member, and the ABS sensor is fixed to the cover member through this pressing portion.
In such a case, it is a common practice to form the cover member and the pressing portion (formed thereon) into an unitary construction to provide a single member. As a result, an opening is inevitably formed in the cover member for covering a magnet rotor, and the magnet rotor is exposed to the exterior. In this case, the formation of the cover member and the pressing portion into the single member causes the exposure of the magnetic member.